| ABSTRACT | Cyclones exhibiting dynamical features similar to the ones of tropical cyclones occur occasionally over the Mediterranean Sea. Mediterranean tropical-like cyclones (MTLC) are characterized by an axis-symmetric vertical profile, a warm core, and a cloud-free eye surrounded by a cloud cover with spiral shape.
A fraction of such storms attain hurricane strength and have thus been termed medicanes (Mediterranean hurricanes). In spite of their small spatial extent and short lifetime -compared to tropical latitudes hurricanes- they are known to produce severe damage when they hit the highly populated Mediterranean Sea coasts.
MTLCs are rare phenomena, and due to the scarcity of observations over sea and the coarse resolution of the long-term reanalysis datasets, it is difficult to construct homogeneous statistics of their formation. Using an approach based on the high-resolution dynamical downscaling of the NCEP/NCAR reanalysis data, and exploiting an objective detection algorithm specifically designed to single out their features, the properties of MTLCs over the last six decades have been studied in a systematic way, and the linkage between the frequency of medicanes formation and synoptic patterns have been investigated.
Differently from tropical-latitudes hurricanes, cold air aloft is required in order to enhance thermodynamic disequilibrium and trigger the formation of Mediterranean tropical-like cyclones. Due to this, the formation of MTLC is found to occur mostly during the cold season in the western Mediterranean and in the region extending between the Ionian Sea and the northern coast of Africa.
Applying the downscaling procedure to the atmospheric fields produced for the last three decades of the century by a global climate model, forced with different future climate scenarios greenhouse gas concentrations, we estimate the impact of climate change on the statistics of Mediterranean tropical-like cyclones.
We find that the frequency of MTLCs is projected to decrease in climate scenarios, as a consequence of the lower frequency of environmental configurations favorable for their formation. The projected intensity of MTLCs detected in future climate simulations shows on the other hand a tendency to a moderate increase. |